<html>
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>变量</title>
</head>
<body>
    
</body>
<script>
    console.log(parseInt(""));   //返回NaN
    console.log(parseInt(3.14));  //返回3
    console.log(parseInt("4.12"));  //返回4
    console.log(parseInt("abc123"));  //返回NaN
    console.log(parseInt("123abc"));   //返回123
</script>
</html>